U.S. patent application number 17/421514 was filed with the patent office on 2022-03-03 for an apparatus for measuring functionality of an arterial system.
The applicant listed for this patent is TURUN YLIOPISTO. Invention is credited to Matti KAISTI, Tero KOIVISTO, Mikko PANKAALA, Tuukka PANULA.
Application Number | 20220061687 17/421514 |
Document ID | / |
Family ID | 1000006024581 |
Filed Date | 2022-03-03 |
United States Patent
Application |
20220061687 |
Kind Code |
A1 |
PANULA; Tuukka ; et
al. |
March 3, 2022 |
AN APPARATUS FOR MEASURING FUNCTIONALITY OF AN ARTERIAL SYSTEM
Abstract
An apparatus for measuring functionality of an arterial system
of an individual includes a photoplethysmography sensor for
emitting, to the arterial system, electromagnetic radiation having
a wavelength in the range from 475 nm to 600 nm and for receiving a
part of the electromagnetic radiation reflected off the arterial
system. The apparatus further includes a pressure instrument for
managing mechanical pressure applied on the arterial system when
the photoplethysmography sensor emits and receives the
electromagnetic radiation to and from the arterial system. The
effect of the mechanical pressure on the envelope of the reflected
electromagnetic radiation can be used for determining diastolic
blood pressure of arteries or for determining whether there is
normal endothelial function.
Inventors: |
PANULA; Tuukka; (Turun
yliopisto, FI) ; KAISTI; Matti; (Turun yliopisto,
FI) ; PANKAALA; Mikko; (Turun yliopisto, FI) ;
KOIVISTO; Tero; (Turun yliopisto, FI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TURUN YLIOPISTO |
Turun yliopisto |
|
FI |
|
|
Family ID: |
1000006024581 |
Appl. No.: |
17/421514 |
Filed: |
November 13, 2019 |
PCT Filed: |
November 13, 2019 |
PCT NO: |
PCT/FI2019/050807 |
371 Date: |
July 8, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 5/02416 20130101;
A61B 5/02241 20130101; A61B 5/6843 20130101; A61B 5/02255 20130101;
A61B 5/02141 20130101; A61B 5/6826 20130101; A61B 5/14551 20130101;
A61B 5/02108 20130101 |
International
Class: |
A61B 5/024 20060101
A61B005/024; A61B 5/021 20060101 A61B005/021; A61B 5/022 20060101
A61B005/022; A61B 5/0225 20060101 A61B005/0225; A61B 5/1455
20060101 A61B005/1455; A61B 5/00 20060101 A61B005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 9, 2019 |
FI |
20195009 |
Claims
1. An apparatus for measuring functionality of an arterial system
of an individual, the apparatus comprising a photoplethysmography
sensor for emitting, to the arterial system, electromagnetic
radiation having a wavelength in a range from 475 nm to 600 nm and
for receiving a part of the electromagnetic radiation reflected off
the arterial system, wherein the apparatus further comprises a
pressure instrument for managing mechanical pressure applied on the
arterial system when the photoplethysmography sensor emits and
receives the electromagnetic radiation to and from the arterial
system.
2. The apparatus according to claim 1, wherein the pressure
instrument is suitable for changing the mechanical pressure applied
on the arterial system when the photoplethysmography sensor emits
and receives the electromagnetic radiation to and from the arterial
system.
3. The apparatus according to claim 2, wherein the pressure
instrument comprises a pressing element for directing the
mechanical pressure to a fingertip of the individual and for
changing the mechanical pressure when the photoplethysmography
sensor emits and receives the electromagnetic radiation to and from
the fingertip.
4. The apparatus according to claim 1, wherein the apparatus
comprises a processing system for determining a first value of the
mechanical pressure at which an envelope of the reflected
electromagnetic radiation reaches a maximum when the mechanical
pressure is ramped from a start value to an end value, the
determined first value being indicative of mean arterial pressure
of arterioles of the arterial system.
5. The apparatus according to claim 4, wherein the processing
system is configured to determine a second value of the mechanical
pressure which is higher than the determined first value and at
which the envelope of the reflected electromagnetic radiation is
substantially a predetermined percentage of the maximum, the
determined second value being indicative of diastolic blood
pressure of arteries of the arterial system as well as systolic
blood pressure of the arterioles of the arterial system.
6. The apparatus according to claim 2, wherein the apparatus
comprises a processing system for controlling the pressure
instrument to increase the mechanical pressure until an envelope of
the reflected electromagnetic radiation drops down to substantially
zero and subsequently to keep the mechanical pressure constant.
7. The apparatus according to claim 6, wherein the processing
system is configured to detect whether the envelope of the
reflected electromagnetic radiation increases when the mechanical
pressure is kept constant, an increase of the envelope being
indicative of normal endothelial function of the arterial
system.
8. The apparatus according to claim 1, wherein the pressure
instrument comprises a pressure sensor for measuring pressure
directed by a fingertip of the individual to the pressure sensor
when the photoplethysmography sensor emits and receives the
electromagnetic radiation to and from the fingertip.
9. The apparatus according to claim 8, wherein the apparatus is a
part of a mobile device and the pressure sensor and the
photoplethysmography sensor are on a surface of the mobile
device.
10. The apparatus according to claim 1, wherein the wavelength of
the electromagnetic radiation is in the range from 500 nm to 600
nm.
11. The apparatus according to claim 1, wherein the wavelength of
the electromagnetic radiation is in the range from 500 nm to 550
nm.
12. The apparatus according to claim 1, wherein the electromagnetic
radiation having the wavelength in the range from 475 nm to 600 nm
is first electromagnetic radiation, and the photoplethysmography
sensor is configured to emit, to the arterial system, second
electromagnetic radiation having a wavelength in a range from 620
nm to 900 nm and to receive a part of the second electromagnetic
radiation reflected off the arterial system.
13. An The apparatus according to claim 12, wherein the apparatus
comprises a processing system for determining a third value of the
mechanical pressure at which an envelope of the reflected second
electromagnetic radiation reaches a maximum when the mechanical
pressure is ramped from a start value to an end value, the
determined third value being indicative of mean arterial pressure
of arteries of the arterial system.
14. The apparatus according to claim 13, wherein the processing
system is configured to determine a fourth value of the mechanical
pressure which is higher than the determined third value and at
which the envelope of the reflected second electromagnetic
radiation is substantially a first predetermined percentage of the
maximum of the envelope of the reflected second electromagnetic
radiation, the determined fourth value being indicative of systolic
blood pressure of arteries of the arterial system.
15. The apparatus according to claim 12, wherein the apparatus
comprises a processing system for controlling the pressure
instrument to increase the mechanical pressure until a maximum of
the envelope of the reflected second electromagnetic radiation is
reached and subsequently to keep the mechanical pressure
constant.
16. The apparatus according to claim 2, wherein the pressure
instrument comprises a pressing device for directing the mechanical
pressure to a brachial artery of the individual, and wherein the
photoplethysmography sensor is located on a surface of the pressing
device intended to be on top of the brachial artery.
17. The apparatus according to claim 16, wherein the pressing
device is a cuff and the pressure instrument comprises a pump
system for controlling gas pressure inside the cuff to direct the
mechanical pressure to the brachial artery, and wherein the
photoplethysmography sensor is located on an inner surface of the
cuff.
18. A method for measuring functionality of an arterial system of
an individual, the method comprising: emitting, to the arterial
system, electromagnetic radiation having a wavelength in a range
from 475 nm to 600 nm, receiving a part of the electromagnetic
radiation reflected off the arterial system, producing information
indicative of the functionality of the arterial system based on the
received electromagnetic radiation, and changing mechanical
pressure applied on the arterial system when the electromagnetic
radiation is emitted to the arterial system and the reflected
electromagnetic radiation is received from the arterial system.
19. A non-transitory computer readable medium on which is stored a
computer program comprising computer executable instructions which,
when executed by a programmable processing system, cause the
programmable processing system perform steps of: controlling a
photoplethysmography sensor to emit, to the arterial system,
electromagnetic radiation having a wavelength in a range from 475
nm to 600 nm, and to receive a part of the electromagnetic
radiation reflected off the arterial system, and controlling a
pressure instrument to manage mechanical pressure applied on the
arterial system when the photoplethysmography sensor emits and
receives the electromagnetic radiation to and from the arterial
system.
20. The non-transitory computer readable medium according to claim
19, wherein the computer program comprises computer executable
instructions for controlling the programmable processing system to
control the pressure instrument to change the mechanical pressure
applied on the arterial system when the photoplethysmography sensor
emits and receives the electromagnetic radiation to and from the
arterial system.
21. (canceled)
Description
FIELD OF THE DISCLOSURE
[0001] The disclosure relates to an apparatus and a method for
measuring functionality of an arterial system. The measured
functionality can be for example diastolic blood pressure "DBP" of
arteries or an endothelial function that describes the ability of
blood circulation to react to vasomotoric changes. Furthermore, the
disclosure relates to a computer program for measuring
functionality of an arterial system.
BACKGROUND
[0002] Abnormalities that may occur in an arterial system, if not
diagnosed and appropriately treated and/or remedied, may
progressively decrease the health of an individual. For example,
elevated blood pressure is a significant risk factor for
cardiovascular diseases. Therefore, a blood pressure measurement is
a routine task in many medical examinations. Automated Non-Invasive
Blood Pressure "NIBP" measurement techniques, a typical being the
oscillometric method, have been around for decades. In this
technique, a cuff is placed on top of the brachial artery and, when
air is pumped into the cuff to exceed the systolic pressure, the
flow of blood is completely blocked. When the air pressure in the
cuff is released, pulsations i.e. oscillations measured in the cuff
increase to the point of mean arterial pressure "MAP" and start to
decrease after this. A bell-shaped envelope of the pulsations is
presented in the time domain along with the corresponding
decreasing pressure curve. Systolic and diastolic blood pressures
are then computed from the MAP using pre-fixed percentages derived
from population studies. The systolic blood pressure is typically
deemed to correspond to a point of the pressure curve where the
pressure is higher than the MAP and a value of the envelope is 50%
of the maximum of the envelope i.e. 50% of the value of the
envelope corresponding to the MAP, and the diastolic blood pressure
is typically deemed to correspond to a point of the pressure curve
where the pressure is lower than the MAP and a value of the
envelope is 80% of the maximum of the envelope.
[0003] Another example of abnormalities in an arterial system is
endothelial dysfunction that is concerned to be a precursor state
for atherosclerosis, which is caused by formation of plaque in
arteries. In clinical tests endothelial function is triggered by
occluding the brachial artery for several minutes, and when
released, the flow of blood in to the arteries increases and the
endothelial cells start to excrete nitric oxide NO. The nitric
oxide then causes the arteries to dilate letting more blood flow
through. Arteries with endothelial dysfunction do not dilate in the
same way.
[0004] In many cases it is advantageous that abnormalities of the
kind described above are detected at an early stage. Therefore,
there is a need for easy-to-use techniques for e.g. measuring blood
pressure and/or for obtaining indications of endothelial
dysfunction.
SUMMARY
[0005] The following presents a simplified summary in order to
provide a basic understanding of some aspects of various invention
embodiments. The summary is not an extensive overview of the
invention. It is neither intended to identify key or critical
elements of the invention nor to delineate the scope of the
invention. The following summary merely presents some concepts of
the invention in a simplified form as a prelude to a more detailed
description of exemplifying embodiments of the invention.
[0006] In accordance with the invention, there is provided a new
apparatus for measuring functionality of an arterial system of an
individual. An apparatus according to the invention comprises a
photoplethysmography "PPG" sensor for emitting, to the arterial
system, electromagnetic radiation having a wavelength in the range
from 475 nm to 600 nm and for receiving a part of the
electromagnetic radiation reflected off the arterial system. The
apparatus further comprises a pressure instrument for managing
mechanical pressure applied on the arterial system when the
photoplethysmography sensor emits and receives the electromagnetic
radiation to and from the arterial system.
[0007] In this document, the verb "to manage" is to be understood
in a broad sense so that managing does not necessarily comprise
controlling or changing an entity being managed, e.g. the
above-mentioned mechanical pressure, but the managing may comprise
only measuring the managed entity.
[0008] The above-mentioned wavelength range from 475 nm to 600 nm
has been selected so that the above-mentioned electromagnetic
radiation does not reach the arteries located in the hypodermis but
can only reach the more superficial dermal arterioles located in
the reticular dermis. The wavelength can be, for example but not
necessarily, circa 537 nm in which case the electromagnetic
radiation is green light.
[0009] The pulse pressure, i.e. the difference between systolic and
diastolic blood pressures, increases from the brachial artery
located in an upper arm to the radial artery located in a wrist to
the transverse palmar arch artery located in a fingertip. When
entering the arterioles and finally the capillaries, the mean
arterial pressure "MAP" and the pulse pressure drop significantly.
In has been noticed that the diastolic blood pressure in the
arteries of a fingertip equals substantially the systolic blood
pressure of the arterioles of the fingertip. Thus, the
above-described apparatus can be used for measuring the MAP in the
arterioles and the systolic blood pressure in the arterioles, as
well as for estimating the diastolic blood pressure in the
arteries. A measurement routine may comprise, for example but not
necessarily, ramping mechanical pressure applied on a fingertip and
recoding the output signal of the PPG sensor. The output signal of
the PPG sensor is indicative of electromagnetic radiation reflected
off the arterioles of the fingertip. The MAP corresponds to a value
of the mechanical pressure at which the envelope of the reflected
electromagnetic radiation reaches its maximum. The systolic blood
pressure in the arterioles and the diastolic blood pressure in the
arteries correspond to a value of the mechanical pressure which is
greater than the MAP and at which the envelope of the reflected
electromagnetic radiation is a predetermined percentage, e.g. 50%,
of the maximum. The ramping the mechanical pressure may comprise
for example pressing the finger above systolic blood pressure so
that the blood flow is blocked and then slowly reducing the press.
It is also possible that the mechanical pressure is increased from
zero up to a point at which the blood flow is blocked. The envelope
of the reflected electromagnetic radiation can be formed by e.g.
bandpass filtering the output signal of the PPG sensor and by
constructing an envelope curve of the bandpass filtered output
signal.
[0010] For another example, the above-described apparatus can be
used for measuring endothelial function. A measurement routine may
comprise, for example but not necessarily, increasing mechanical
pressure applied on a fingertip until the envelope of the reflected
electromagnetic radiation gets nearly zero and then keeping the
mechanical pressure constant. In a case of proper endothelial
function, an increase in the envelope of the reflected
electromagnetic radiation can be seen when the mechanical pressure
is kept constant. In a case of endothelial dysfunction, no increase
of the kind mentioned above takes place.
[0011] In an apparatus according to an exemplifying and
non-limiting embodiment, the PPG sensor comprises means for
emitting, to an arterial system, second electromagnetic radiation
having a wavelength in the range from 620 nm to 900 nm in addition
to the above-mentioned first electromagnetic radiation having the
wavelength in the range from 475 nm to 600 nm, and means for
receiving parts of the above-mentioned first and second
electromagnetic radiations reflected off the arterial system.
[0012] The wavelength range of the second electromagnetic radiation
from 620 nm to 900 nm has been selected so that the second
electromagnetic radiation reach the arteries located in the
hypodermis. Thus, the second electromagnetic radiation can be used
for measuring the MAP in the arteries, the systolic blood pressure
in the arteries, as well as the diastolic blood pressure in the
arteries. Thus, the diastolic blood pressure in the arteries can be
measured with both the first and second electromagnetic radiations,
which improve the accuracy and reliability of the measurement. A
measurement routine may comprise, for example but not necessarily,
ramping mechanical pressure applied on a fingertip and recoding,
from the PPG sensor, first and second output signals corresponding
to the first and second electromagnetic radiations reflected off
the arterial system of the fingertip. For another example, the
second electromagnetic radiation can be used for determining a
point up to which the mechanical pressure applied on a fingertip is
increased when measuring endothelial function. In this measurement,
the mechanical pressure is increased until the envelope of the
reflected second electromagnetic radiation reaches its maximum. The
wavelength of the second electromagnetic radiation can be, for
example but not necessarily, circa 660 nm in which case the second
electromagnetic radiation is red light or circa 880 nm in which
case the second electromagnetic radiation is infrared "IR"
radiation.
[0013] In accordance with the invention, there is provided a new
method for measuring functionality of an arterial system of an
individual. A method according to the invention comprises: [0014]
emitting, to the arterial system, electromagnetic radiation having
a wavelength in the range from 475 nm to 600 nm, [0015] receiving a
part of the electromagnetic radiation reflected off the arterial
system, [0016] changing mechanical pressure applied on the arterial
system when the electromagnetic radiation is emitted to the
arterial system and the reflected electromagnetic radiation is
received from the arterial system, and [0017] producing information
indicative of the functionality of the arterial system based on the
received electromagnetic radiation.
[0018] In accordance with the invention, there is provided also a
new computer program for measuring functionality of an arterial
system of an individual. A computer program according to the
invention comprises computer executable instructions for
controlling a programmable processing system to: [0019] control a
photoplethysmography sensor to emit, to the arterial system,
electromagnetic radiation having a wavelength in the range from 475
nm to 600 nm, and to receive a part of the electromagnetic
radiation reflected off the arterial system, and [0020] control a
pressure instrument to manage mechanical pressure applied on the
arterial system when the photoplethysmography sensor emits and
receives the electromagnetic radiation to and from the arterial
system.
[0021] In accordance with the invention, there is provided also a
new computer program product. The computer program product
comprises a non-volatile computer readable medium, e.g. a compact
disc "CD", encoded with a computer program according to the
invention.
[0022] Exemplifying and non-limiting embodiments are described in
accompanied dependent claims.
[0023] Various exemplifying and non-limiting embodiments both as to
constructions and to methods of operation, together with additional
objects and advantages thereof, will be best understood from the
following description of specific exemplifying embodiments when
read in conjunction with the accompanying drawings.
[0024] The verbs "to comprise" and "to include" are used in this
document as open limitations that neither exclude nor require the
existence of also un-recited features.
[0025] The features recited in the accompanied dependent claims are
mutually freely combinable unless otherwise explicitly stated.
Furthermore, it is to be understood that the use of "a" or "an",
i.e. a singular form, throughout this document does not exclude a
plurality.
BRIEF DESCRIPTION OF FIGURES
[0026] Exemplifying and non-limiting embodiments and their
advantages are explained in greater detail below with reference to
the accompanying drawings, in which:
[0027] FIG. 1a illustrates an apparatus according to an
exemplifying and non-limiting embodiment for measuring
functionality of an arterial system, FIG. 1 b shows an exemplifying
graph illustrating electromagnetic radiation reflected off an
arterial system of a fingertip as a function of time, and FIG. 1 c
shows a mobile device comprising an apparatus illustrated in FIG. 1
a,
[0028] FIG. 2a illustrates an apparatus according to an
exemplifying and non-limiting embodiment for measuring
functionality of an arterial system, and FIG. 2b shows exemplifying
graphs illustrating electromagnetic radiations having different
wavelengths and reflected off an arterial system of a fingertip as
functions of time,
[0029] FIG. 3 illustrates an apparatus according to an exemplifying
and non-limiting embodiment for measuring functionality of an
arterial system,
[0030] FIG. 4a illustrates an apparatus according to an
exemplifying and non-limiting embodiment for measuring
functionality of an arterial system, and FIG. 4b shows exemplifying
graphs illustrating electromagnetic radiations having different
wavelengths and reflected off an arterial system of a fingertip as
functions of time, and
[0031] FIG. 5 shows a flowchart of a method according to an
exemplifying and non-limiting embodiment for measuring
functionality of an arterial system.
DESCRIPTION OF EXEMPLIFYING AND NON-LIMITING EMBODIMENTS
[0032] The specific examples provided in the description below
should not be construed as limiting the scope and/or the
applicability of the appended claims. Lists and groups of examples
provided in the description are not exhaustive unless otherwise
explicitly stated.
[0033] FIG. 1a shows a schematic illustration of an apparatus
according to an exemplifying and non-limiting embodiment for
measuring functionality of an arterial system. The apparatus
comprises a photoplethysmography "PPG" sensor 101 for emitting, to
a fingertip 108 of an individual, electromagnetic radiation having
a wavelength in the range from 475 nm to 600 nm and for receiving a
part of the electromagnetic radiation reflected off the arterial
system of the fingertip 108. In an apparatus according to an
exemplifying and non-limiting embodiment, the wavelength is in the
range from 480 nm to 600 nm. In an apparatus according to an
exemplifying and non-limiting embodiment, the wavelength is in the
range from 500 nm to 600 nm. In an apparatus according to an
exemplifying and non-limiting embodiment, the wavelength is in the
range from 500 nm to 575 nm. In an apparatus according to an
exemplifying and non-limiting embodiment, the wavelength is in the
range from 500 nm to 550 nm. The wavelength can be, for example but
not necessarily, circa 537 nm in which case the electromagnetic
radiation is green light. The PPG sensor 101 comprises a radiation
emitter 109 and a photodetector 110. The radiation emitter 109 can
be e.g. a light emitting diode "LED" and the photodetector 110 can
be e.g. a photodiode or a phototransistor. FIG. 1a shows also a
magnified, schematic section view 130 of the fingertip. The section
plane is parallel with the yz-plane of a coordinate system 199. In
the section view 130, the emitted and reflected radiation is
depicted with a polyline 117. As illustrated in the section view
130, the electromagnetic radiation 117 does not reach arteries 111
located in the hypodermis 114 but can only reach arterioles 112
located in the reticular dermis 115. In the section view 130,
capillaries are denoted with a reference 113 and the epidermis of
the skin of the fingertip is denoted with a reference 116.
[0034] The apparatus further comprises a pressure instrument 102
for managing mechanical pressure applied on the arterial system
when the photoplethysmography sensor 101 emits and receives the
electromagnetic radiation. In this exemplifying case, the pressure
instrument 102 comprises a pressure sensor for measuring mechanical
pressure P directed by the fingertip 108 to the pressure
sensor.
[0035] FIG. 1b shows a curve 119 that illustrates the reflected
electromagnetic radiation in an exemplifying situation where the
apparatus is used for estimating the mean arterial pressure "MAP"
in the arterioles 112, the systolic blood pressure "SYS" in the
arterioles, as well as the diastolic blood pressure "DIA" in the
arteries 111. In this exemplifying case, the fingertip 108 is first
pressed against the pressure instrument 102 so that the mechanical
pressure P is above the systolic blood pressure and thus the blood
flow is blocked. Thereafter, the press is slowly released so that
the mechanical pressure P is ramped down as a function of time as
depicted with a curve 122 shown in FIG. 1b. The curve 119 may
represent for example a bandpass filtered output signal of the PPG
sensor 101. The passband of the bandpass filtering can be from
example from 1 Hz to 10 Hz. In this exemplifying case, the bandpass
filtered signal is Hilbert transformed for forming an envelope of
the bandpass filtered signal. In FIG. 1b, the Hilbert transformed
filtered signal is depicted with a curve 120 and the envelope is
depicted with a curve 121.
[0036] An estimate of the MAP in the arterioles 112 is the value of
the mechanical pressure P where the above-mentioned envelope 121 of
the reflected electromagnetic radiation reaches its maximum. Thus,
the MAP in the arterioles can be estimated with the aid of the
envelope curve 121 and the mechanical pressure curve 122 as shown
in FIG. 1b. An estimate of the systolic blood pressure "SYS" in the
arterioles 112 is the value of the mechanical pressure P which is
greater than the estimated MAP in the arterioles 112 and at which
the envelope of the reflected electromagnetic radiation is a
predetermined percentage, typically 50%, of the maximum of the
envelope. Thus, the SYS in the arterioles can be estimated with the
aid of the envelope curve 121 and the mechanical pressure curve 122
as shown in FIG. 1b. The estimate of the SYS in the arterioles is
also an estimate of the diastolic blood pressure "DIA" in the
arteries 111.
[0037] In the exemplifying case illustrated in FIG. 1b, the
mechanical pressure P is ramped down. It is however also possible
that the mechanical pressure P is ramped up for estimating the MAP
in the arterioles 112, the SYS in the arterioles, and the DIA in
the arteries 111. In this exemplifying case, the envelope of the
reflected electromagnetic radiation is a time-reversed version of
the envelope 121. Furthermore, it is to be noted that the
mechanical pressure P does not necessarily follow an ideal straight
line as a function of time when the mechanical pressure P is ramped
down or up.
[0038] An apparatus according to an exemplifying and non-limiting
embodiment comprises a processing system 103 configured to
determine the estimate of the MAP in the arterioles 112. In other
words, the processing system 103 is configured to determine a first
value of the mechanical pressure P where the above-mentioned
envelope 121 of the reflected electromagnetic radiation reaches its
maximum when the mechanical pressure P is ramped down or up from a
start value to an end value, the first value being the estimate of
the MAP in the arterioles 112. In an apparatus according to an
exemplifying and non-limiting embodiment, the processing system 103
is configured to determine the estimate of the SYS in the
arterioles 112 and the estimate of the DIA in the arteries 111. In
other words, the processing system 103 is configured to determine a
second value of the mechanical pressure P which is higher than the
determined first value and at which the envelope of the reflected
electromagnetic radiation is substantially a predetermined
percentage, typically 50%, of the maximum of the envelope, the
determined second value being the estimate of the SYS in the
arterioles 112 and the estimate of the DIA in the arteries 111. It
is however also possible that an apparatus according to an
exemplifying and non-limiting embodiment comprises a memory for
storing time-series of the output signals of the PPG sensor and the
pressure sensor, and/or a transmitter for transmitting the
time-series to an external device. In this exemplifying case, the
above-mentioned estimates that describe functionality of an
arterial system can be formed off-line with an external device,
e.g. a personal computer.
[0039] FIG. 1c shows a mobile device 107 comprising the apparatus
illustrated in FIG. 1a. The mobile device 107 can be for example a
mobile phone or a palmtop computer. The pressure sensor and the PPG
sensor are on a surface of the mobile device so that an individual
can press a fingertip 108 against the pressure sensor and the PPG
sensor. In this exemplifying case, the mobile device 107 is
configured to display the bandpass filtered output signal of the
PPG sensor and the envelope of the bandpass filtered output signal.
Furthermore, the mobile device 107 is configured to display the
estimates of the SYS in the arterioles, the MAP in the arterioles,
and the DIA in the arteries, where the estimates are formed with
the aid of the envelope and time dependence of the mechanical
pressure measured by the pressure sensor. It is also possible that
an apparatus according to an exemplifying embodiment of the
invention is a part of a ring, a bracelet, a wrist watch, or any
other wearable device, or a combination of them, or a combination
of a wearable device and a mobile phone or another mobile
communication device. For example, an inner surface of a ring or a
bracelet can be provided with the PPG sensor and with a pressure
sensor. In this exemplifying case, a user can control the pressure
by pressing the ring or bracelet against a surface of a finger or a
wrist surrounded by the ring or the bracelet.
[0040] FIG. 2a shows a schematic illustration of an apparatus
according to an exemplifying and non-limiting embodiment for
measuring functionality of an arterial system. The apparatus
comprises a photoplethysmography "PPG" sensor 201 for emitting, to
a fingertip 208 of an individual, first electromagnetic radiation
having a wavelength in the range from 475 nm to 600 nm and second
electromagnetic radiation having a wavelength in the range from 620
nm to 900 nm, and for receiving parts of the first and second
electromagnetic radiations reflected off the arterial system of the
fingertip 208. The wavelength of the first electromagnetic
radiation can be, for example but not necessarily, circa 537 nm in
which case the first electromagnetic radiation is green light. In
an apparatus according to an exemplifying and non-limiting
embodiment, the wavelength of the second electromagnetic radiation
is in the range from 650 nm to 890 nm. The wavelength of the second
electromagnetic radiation can be, for example but not necessarily,
circa 660 nm in which case the second electromagnetic radiation is
red light or circa 880 nm in which case the second electromagnetic
radiation is infrared "IR" radiation.
[0041] It is also possible that the PPG sensor 201 is configured to
emit and measure electromagnetic radiation with three or more
different wavelengths. The PPG sensor 201 comprises a radiation
emitter 209 and a photodetector 210. The radiation emitter 209 may
comprise e.g. light emitting diodes "LED" and the photodetector 110
may comprise e.g. wavelength sensitive photodiodes or
phototransistors. FIG. 2a shows also a magnified, schematic section
view 230 of the fingertip. The section plane is parallel with the
yz-plane of a coordinate system 299. In the section view 230, the
first emitted and reflected electromagnetic radiation is depicted
with a polyline 217 and the second emitted and reflected
electromagnetic radiation is depicted with a polyline 218. As
illustrated in the section view 230, the first electromagnetic
radiation 217 does not reach arteries 111 located in the hypodermis
114 but can only reach arterioles 112 located in the reticular
dermis 115 whereas the second electromagnetic radiation 218 can
reach the arteries 111. In the section view 230, capillaries are
denoted with a reference 113 and the epidermis of the skin of the
fingertip is denoted with a reference 116.
[0042] The apparatus further comprises a pressure instrument for
managing mechanical pressure applied on the arterial system when
the PPG sensor 201 emits and receives the above-mentioned first and
second electromagnetic radiations. In this exemplifying case, the
pressure instrument comprises a pressure sensor 202a for measuring
mechanical pressure P directed by the fingertip 208 to the pressure
sensor and pressing means 202b for controllably pressing the
fingertip 208 against the PPG sensor 201 and the pressure sensor
202a. In this exemplifying apparatus, the pressing means comprise a
pressing element 204 and force generating means 228 for directing
force to the pressing element 204. The force generating means 228
may comprise for example an electric stepper motor and a threaded
rod.
[0043] FIG. 2b shows a curve 219 that illustrates the reflected
first electromagnetic radiation and a curve 223 that illustrates
the reflected second electromagnetic radiation in an exemplifying
situation where the apparatus is used for estimating the mean
arterial pressure "MAP1" in the arterioles 112, the mean arterial
pressure "MAP2" in the arteries 111, the systolic blood pressure
"SYS1" in the arterioles, the systolic blood pressure "SYS2" in the
arteries, and the diastolic blood pressure "DIA2" in the arteries.
In this exemplifying case, the fingertip 208 is first pressed
against the pressure sensor 202a so that the mechanical pressure P
is above the systolic blood pressure and thus the blood flow is
blocked. Thereafter, the press is slowly released so that the
mechanical pressure P is ramped down as a function of time as
depicted with a curve 222 shown in FIG. 2b. The curves 219 and 223
may represent for example bandpass filtered output signals of the
PPG sensor 201. The passband of the bandpass filtering can be e.g.
from 1 Hz to 10 Hz. In this exemplifying case, the bandpass
filtered signals are Hilbert transformed for forming envelopes of
the bandpass filtered signals. In FIG. 2b, the Hilbert transformed
filtered signals are depicted with dashed line curves. The envelope
of the reflected first electromagnetic radiation is depicted with a
curve 221, and the envelope of the reflected second electromagnetic
radiation is depicted with a curve 224.
[0044] As shown by FIG. 2b, the estimate of the MAP1 is the value
of the mechanical pressure P where the envelope 221 reaches its
maximum, the estimate of the MAP2 is the value of the mechanical
pressure P where the envelope 224 reaches its maximum, the estimate
of the SYS1 is the value of the mechanical pressure P which is
greater than the MAP1 and at which the envelope 221 is 50% of the
maximum of the envelope 221, the estimate of the SYS2 is the value
of the mechanical pressure P which is greater than the MAP2 and at
which the envelope 224 is 50% of the maximum of the envelope 224,
and the estimate of the DIA2 is the value of the mechanical
pressure P which is less than the MAP2 and at which the envelope
224 is 80% of the maximum of the envelope 224. As the systolic
blood pressure SYS1 in the arterioles is substantially equal to the
diastolic blood pressure DIA2 in the arteries, the estimate of the
SYS1 acts as another estimate for the diastolic blood pressure in
the arteries. A final estimate for the diastolic blood pressure in
the arteries can be for example a weighted average of the estimate
based on the envelope 224 and the estimate based on the envelope
221.
[0045] An apparatus according to an exemplifying and non-limiting
embodiment comprises a processing system 203 configured to control
the force generating means 228 so that the mechanical pressure P
has a desired behavior as a function of time, e.g. such as depicted
with the curve 222 in FIG. 2b. Furthermore, the processing system
203 can be configured to form the above-mentioned estimates with
the aid of the output signals of the PPG sensor 201 and the output
signal of the pressure sensor 202b.
[0046] FIG. 3 shows a schematic illustration of an apparatus
according to an exemplifying and non-limiting embodiment for
measuring functionality of an arterial system. The apparatus
comprises a photoplethysmography "PPG" sensor 301 for emitting, to
the arterial system, electromagnetic radiation having a wavelength
in the range from 475 nm to 600 nm and for receiving a part of the
electromagnetic radiation reflected off the arterial system. The
wavelength can be for example circa 515 nm. The apparatus comprises
a pressure instrument 302 for managing mechanical pressure applied
on the arterial system when the photoplethysmography sensor 301
emits and receives the electromagnetic radiation to and from the
arterial system. In this exemplifying case, the pressure instrument
302 comprises a pressing device 305 for directing controllable
mechanical pressure to the brachial artery. The pressing device 305
can be for example a cuff and the apparatus may comprise a pump
system 306 for controlling gas, e.g. air, pressure inside the cuff
to direct the controllable mechanical pressure to the brachial
artery. It is however also possible that the pressing device
comprises e.g. a flexible belt that is tightened around the upper
arm. The PPG sensor 301 is located on a surface of the pressing
device 305 so that the PPG sensor 301 can be placed on top of the
brachial artery. The brachial artery can be found by e.g.
palpation. According to experiments, an output signal of the PPG
sensor 301 does not show pulsatile waveform when the mechanical
pressure is above diastolic blood pressure and the output signal of
the PPG sensor 301 starts showing pulsatile waveform when the
mechanical pressure is lowered under the diastolic blood pressure.
Thus, the apparatus can be used for direct measurement of the
diastolic blood pressure.
[0047] An apparatus according to an exemplifying and non-limiting
embodiment comprises a processing system 303 configured to control
the pressing device 305 so that the mechanical pressure has a
desired behavior as a function of time. In the exemplifying case
shown in FIG. 3, the processing system 303 is configured to control
the pump system 306 so that the mechanical pressure produced by the
cuff has a desired behavior as a function of time. Furthermore, the
processing system 303 can be configured to determine a value of the
mechanical pressure at which the output signal of the PPG sensor
301 starts showing pulsatile waveform.
[0048] FIG. 4a shows a schematic illustration of an apparatus
according to an exemplifying and non-limiting embodiment for
measuring functionality of an arterial system. The apparatus
comprises a photoplethysmography "PPG" sensor 401 for emitting, to
a fingertip 408 of an individual, first electromagnetic radiation
having a wavelength in the range from 475 nm to 600 nm and second
electromagnetic radiation having a wavelength in the range from 620
nm to 900 nm, and for receiving parts of the first and second
electromagnetic radiations reflected off the arterial system of the
fingertip 408. The wavelength of the first electromagnetic
radiation can be, for example but not necessarily, circa 537 nm in
which case the first electromagnetic radiation is green light. The
wavelength of the second electromagnetic radiation can be for
example circa 660 nm in which case the second electromagnetic
radiation is red light or circa 880 nm in which case the second
electromagnetic radiation is infrared "IR" radiation. The PPG
sensor 401 comprises a radiation emitter 409 and a photodetector
410.
[0049] The apparatus further comprises a pressure instrument 402
for managing mechanical pressure applied on the arterial system
when the PPG sensor 401 emits and receives the first and second
electromagnetic radiation to and from the fingertip 408. In this
exemplifying case, the pressure instrument 402 comprises a pressing
element 404 for pressing the fingertip 408 and force generating
means 428 for directing force to the pressing element 404.
[0050] FIG. 4b shows a curve 425 that illustrates the reflected
first electromagnetic radiation and a curve 426 that illustrates
the reflected second electromagnetic radiation in an exemplifying
situation where the pressure instrument 402 first increases the
mechanical pressure and then keeps the mechanical pressure
substantially constant. The curves 425 and 426 can depict for
example bandpass filtered output signals of the PPG sensor 401. The
passband of the bandpass filtering can be from example from 1 Hz to
10 Hz. The mechanical pressure as a function of time is depicted
with a curve 427 shown in FIG. 4b. As shown by FIG. 4b, the
mechanical pressure is increased up to a point at which the
pulsatile waveform of the reflected first electromagnetic radiation
drops near to zero and the pulsatile waveform of the reflected
second electromagnetic radiation reaches its maximum. The low
pulsatile waveform of the reflected first electromagnetic radiation
indicates near occlusion of arterioles suggesting near systolic
arteriole pressure. Tangential stress caused by small flow triggers
excretion of nitric oxide "NO" in endothelial cells, which then
causes vasodilation in the arterioles letting more blood flow in
them. When the applied mechanical pressure is kept constant, the
pulsatile waveform of the reflected first electromagnetic radiation
increases as illustrated by the curve 425. The above-described
increase in the pulsatile waveform of the reflected first
electromagnetic radiation suggests normal endothelial function,
whereas a lack of increase suggests endothelial dysfunction.
[0051] An apparatus according to an exemplifying and non-limiting
embodiment comprises a processing system 403 for controlling the
pressure instrument 402 to increase the mechanical pressure until
an envelope of the reflected first electromagnetic radiation drops
down to substantially zero and subsequently to keep the mechanical
pressure constant. In an apparatus according to another
exemplifying and non-limiting embodiment, the processing system 403
is configured to control the pressure instrument 402 to increase
the mechanical pressure until an envelope of the reflected second
electromagnetic radiation reaches its maximum and subsequently to
keep the mechanical pressure constant. The force generating means
428 may comprise for example a threaded rod and an electric stepper
motor controlled by the processing system 403. The mechanical
pressure can be increased by running the electric stepper motor in
an appropriate direction of rotation, and the mechanical pressure
can be kept constant by keeping the electric stepper motor
stationary. In an apparatus according to an exemplifying and
non-limiting embodiment, the processing system 403 is configured to
detect whether the envelope of the reflected first electromagnetic
radiation increases when the mechanical pressure is kept
constant.
[0052] Each of the processing systems 103, 203, 303, and 403 shown
in FIGS. 1a, 2a, 3, and 4a can be implemented for example with one
or more processor circuits, each of which can be a programmable
processor circuit provided with appropriate software, a dedicated
hardware processor such as for example an application specific
integrated circuit "ASIC", or a configurable hardware processor
such as for example a field programmable gate array "FPGA". Each of
the processing systems 103, 203, 303, and 403 may further comprise
memory implemented for example with one or more memory circuits
each of which can be e.g. a random-access memory "RAM" device.
[0053] FIG. 5 shows a flowchart of a method according to an
exemplifying and non-limiting embodiment for measuring
functionality of an arterial system of an individual. The method
comprises the following actions: [0054] action 501: emitting, to
the arterial system, electromagnetic radiation having a wavelength
in a range from 475 nm to 600 nm, [0055] action 502: receiving a
part of the electromagnetic radiation reflected off the arterial
system, and [0056] action 503: changing mechanical pressure applied
on the arterial system when the electromagnetic radiation is
emitted to the arterial system and the reflected electromagnetic
radiation is received from the arterial system, and [0057] action
504: producing information indicative of the functionality of the
arterial system based on the received electromagnetic
radiation.
[0058] In a method according to an exemplifying and non-limiting
embodiment the wavelength of the electromagnetic radiation is in
the range from 480 nm to 600 nm.
[0059] In a method according to an exemplifying and non-limiting
embodiment, the wavelength of the electromagnetic radiation is in
the range from 500 nm to 600 nm.
[0060] In a method according to an exemplifying and non-limiting
embodiment, the wavelength of the electromagnetic radiation is in
the range from 500 nm to 575 nm
[0061] In a method according to an exemplifying and non-limiting
embodiment, the wavelength of the electromagnetic radiation is in
the range from 500 nm to 550 nm.
[0062] A method according to an exemplifying and non-limiting
embodiment comprises determining a first value of the mechanical
pressure at which an envelope of the reflected electromagnetic
radiation reaches its maximum when the mechanical pressure is
ramped down or up from a start value to an end value. The
determined first value is indicative of the mean arterial pressure
"MAP" of arterioles of the arterial system.
[0063] A method according to an exemplifying and non-limiting
embodiment comprises determining a second value of the mechanical
pressure which is higher than the determined first value and at
which the envelope of the reflected electromagnetic radiation is
substantially a predetermined percentage e.g. 50% of the maximum of
the envelop. The determined second value is indicative of the
diastolic blood pressure "DIA" of arteries of the arterial system
as well as the systolic blood pressure "SYS" of the arterioles of
the arterial system.
[0064] A method according to an exemplifying and non-limiting
embodiment comprises increasing the mechanical pressure until the
envelope of the reflected electromagnetic radiation drops down to
substantially zero and subsequently keeping the mechanical pressure
constant. Furthermore, the method according to this exemplifying
and non-limiting embodiment comprises detecting whether the
envelope of the reflected electromagnetic radiation increases when
the mechanical pressure is kept constant. An increase in the
envelope is indicative of normal endothelial function of the
arterial system, whereas a lack of increase in indicative of
endothelial dysfunction.
[0065] A method according to an exemplifying and non-limiting
embodiment comprises directing the mechanical pressure to a
fingertip of the individual when the electromagnetic radiation is
emitted and received to and from the fingertip.
[0066] A method according to an exemplifying and non-limiting
embodiment comprises measuring the pressure directed to the
fingertip when the electromagnetic radiation is emitted and
received to and from the fingertip.
[0067] A method according to an exemplifying and non-limiting
embodiment comprises controlling gas pressure inside a cuff
surrounding an upper arm of the individual to direct the mechanical
pressure to the brachial artery of the individual when the
electromagnetic radiation is emitted and received to and from an
area of the upper arm on top of the brachial artery.
[0068] In a method according to an exemplifying and non-limiting
embodiment, the above-mentioned electromagnetic radiation having
the wavelength in the range from 475 nm to 600 nm is first
electromagnetic radiation, and the method according to this
exemplifying and non-limiting embodiment comprises: [0069]
emitting, to the arterial system, second electromagnetic radiation
having a wavelength in the range from 620 nm to 900 nm, and [0070]
receiving a part of the second electromagnetic radiation reflected
off the arterial system.
[0071] In a method according to an exemplifying and non-limiting
embodiment, the wavelength of the second electromagnetic radiation
is the range from 650 nm to 890 nm.
[0072] A method according to an exemplifying and non-limiting
embodiment comprises determining a third value of the mechanical
pressure at which an envelope of the reflected second
electromagnetic radiation reaches its maximum when the mechanical
pressure is ramped down or up from a start value to an end value.
The determined third value is indicative of mean arterial pressure
"MAP" of arteries of the arterial system.
[0073] A method according to an exemplifying and non-limiting
embodiment comprises determining a fourth value of the mechanical
pressure which is higher than the determined third value and at
which the envelope of the reflected second electromagnetic
radiation is substantially a first predetermined percentage, e.g.
50%, of the maximum of the envelope of the reflected second
electromagnetic radiation. The determined fourth value is
indicative of systolic blood pressure "SYS" of arteries of the
arterial system.
[0074] A method according to an exemplifying and non-limiting
embodiment comprises determining a fifth value of the mechanical
pressure which is lower than the determined third value and at
which the envelope of the reflected second electromagnetic
radiation is substantially a second predetermined percentage, e.g.
80%, of the maximum of the envelope of the reflected second
electromagnetic radiation. The determined fifth value is indicative
of diastolic blood pressure "SYS" of arteries of the arterial
system.
[0075] A method according to an exemplifying and non-limiting
embodiment comprises increasing the mechanical pressure until the
envelope of the reflected second electromagnetic radiation reaches
its maximum and subsequently keeping the mechanical pressure
constant. Furthermore, the method according to this exemplifying
and non-limiting embodiment comprises detecting whether the
envelope of the reflected first electromagnetic radiation increases
when the mechanical pressure is kept constant. An increase in the
envelope of the reflected first electromagnetic radiation is
indicative of normal endothelial function of the arterial
system.
[0076] A computer program according to an exemplifying and
non-limiting embodiment comprises computer executable instructions
for controlling a programmable processing system to carry out
actions related to a method according to any of the above-described
exemplifying and non-limiting embodiments.
[0077] A computer program according to an exemplifying and
non-limiting embodiment comprises software modules for measuring
functionality of an arterial system of an individual. The software
modules comprise computer executable instructions for controlling a
programmable processing system to: [0078] control a
photoplethysmography "PPG" sensor to emit, to the arterial system,
electromagnetic radiation having a wavelength in a range from 475
nm to 600 nm, and to receive a part of the electromagnetic
radiation reflected off the arterial system, and [0079] control a
pressure instrument to manage mechanical pressure applied on the
arterial system when the PPG sensor emits and receives the
electromagnetic radiation to and from the arterial system.
[0080] The software modules can be for example subroutines or
functions implemented with programming tools suitable for the
programmable processing equipment.
[0081] In a computer program according to an exemplifying and
non-limiting embodiment, the software modules comprise computer
executable instructions for controlling the programmable processing
system to control the pressure instrument to change the mechanical
pressure applied on the arterial system when the PPG sensor emits
and receives the electromagnetic radiation to and from the arterial
system.
[0082] A computer program product according to an exemplifying and
non-limiting embodiment comprises a computer readable medium, e.g.
a compact disc "CD", encoded with a computer program according to
an exemplifying embodiment.
[0083] A signal according to an exemplifying and non-limiting
embodiment is encoded to carry information defining a computer
program according to an exemplifying embodiment.
[0084] A computer program according to an exemplifying and
non-limiting embodiment may constitute e.g. a part of a software of
a mobile device, e.g. a smart phone or a wearable device.
[0085] The specific examples provided in the description given
above should not be construed as limiting the scope and/or the
applicability of the appended claims. Lists and groups of examples
provided in the description given above are not exhaustive unless
otherwise explicitly stated.
* * * * *